The present disclosure relates to a developing device and an image forming apparatus provided with the same.
Conventionally, an electrophotographic image forming apparatus such as a printer or a copier includes a photoconductive drum for carrying an electrostatic latent image, a developing device for developing the electrostatic latent image into a toner image by supplying toner to the photoconductive drum and a transfer device for transferring the toner image from the photoconductive drum to a sheet.
The developing device includes a developing roller for supplying toner to the photoconductive drum. The developing roller includes a fixed magnet having a plurality of magnetic poles and a sleeve configured to rotate around the magnet. In a two-component developing method, developer containing toner and magnetic carrier is carried on the sleeve of the developing roller. A developer conveying amount is regulated by a layer thickness regulating member arranged to face the developing roller.
In such a two-component developing method, it is important for stable image quality to stabilize the developer conveying amount on the developing roller. This developer conveying amount is mainly determined by (1) the size of a gap (regulation gap) between the layer thickness regulating member and the developing roller, (2) the density of the developer retained on a side upstream of the layer thickness regulating member, (3) a regulating force by a magnetic force around the layer thickness regulating member, and (4) a developer conveying force by the developing roller.
Conventionally, a technique for concentrating a magnetic force on the layer thickness regulating member is known as a regulating method for stabilizing the above developer conveying amount.